Method of and apparatus for receiving high frequency oscillations



Aug. 29, 1933. E. H. SMYTHE' I 1,924,628 METHOD OF AND APPARATUS FORRECEIVING HIGH FREQUENCY OSCILLATIONS Filed Feb. '8, 1926 3 Sheets-Sheet1 3 Sheets-Sheet 2 E. ,H. SMYTH'E Filed Feb. 8, 1926 6 WI" w ii T 1 -w\V m h 4 NWH WW H \h n 5 v Q flfl d A. N

Aug. 29, 1933.

union or AND APPARATUS FOR RECEIVING HIGH FREQUENCY OSCILLATIONS will"1933. E. H. SMYTHE 1,924,628

METHOD OF AND APPARATUS FOR RECEIVING HIGH FREQUENCY OSCILLATIONS FiledFeb. 8, 1925 Z S m 9? 3 Sheets-Sheet 3 Patented Aug. 29, 193 3 CEIVINGHIGH TIONS FREQUENCY OSCILLA- i Edwin H. Smythe, Evan ston; 111.,assignor to American Telephone and Telegraph Company, a corporation ofNew York Application February ii, 1926. Serial No. 86,811

Claims;

This invention relates toa method of and apparatus for receiving highfrequency 'oscilla tionssuch as are employed inconnectioniwith radiotelephony and radio telegraphy, and parr- ,5 ti'cularly in connectionwith systems of this sort employing continuous or sustainedoscillations. In such systems'it 'is customary to superpose upon thecontinuous oscillationsradiated from the transmitting station,modulations produced by the operation of a telephone transmitter or by atelegraph key." The modulatedoscillations which reach the receivingstation are greatly a ttenuated, and in order that they may be madeeifective to bring about the operation, of the receiving station it isordinarily their energy shall be amplified; There are inherentdifiiculties attendant upon the amplification of the received energy,either '20 before or"v after the modulating componentof the highfrequency oscillations is separated out by the usual detecting orrectifying fproces's.

When the amplification is effected at the high frequency of the receivedoscillations -a'practicouplings and reactions which exist between dif-;ferent parts of the circuits and apparatus, these eifects being greatlyaugmented at the high free communication. When' theamplification'is'effected at frequencies such as areordinarily used inthe modulation of the high frequency radi ated wave, that is, atthe'so-called audio fre quencies; not only are the detectedmodulatin'gfrequencies of the received wave amplified, but also suchlocallyproduced disturbances as tubeno'isesfand the like, so that thepractical limit.

of audio frequency amplification is speedily reached.

r In systems of receptionibaseduponthe heterodyne and superheterodyne'principles, amplifica tion iseffected at an intermediate frequency, thisintermediate frequency being produced by interaction between thereceived high frequency wave and a locallygenerated wave that is also ahigh frequency wave differing in frequencyfrom the received wave by anamount equal to the frequency at which the intermediate amplification isto be effected. The: high frequency of this locally generated wave issuch as to make it a good radiator of energy; and to avoidsuch-radiation of the energyof the locallygenerated wave, whichmay'objectionably'aife'ct the operation of neighboring receiving sets,it is customaryto re-- strict the use of theheterodyne receiver to setsresponsive or si'gnalindicating 'devicesjat the necessary that cal limitis imposed upon it by' the inherent quencies which areordinarily-employed inradio employing loop antennae for the interceptiOn'of l the received high frequency waves. Furthermore, the heterodyneprinciplehas the objectionable feature of complicating' the stationselecting operation dueto the-fact'that each station appears at-twopositions on the dialof the local.

oscillator tuning'condenser. In the method and organizationofthe'presentinvention all of the advantages of amplification-at areadily amplifiable' intermediate frequency are retained, whileat thesame time the complications due to the appearance of each station at twopoints on the tuning dial are avoided, and the'use of anopen I orordinary antenna is made possible by the employment of a locallygenerated oscillation having a frequency such that it may becom-flmunicated to the antenna without giving'riseto disturbance inneighboring receiving sets.

Generally stated; the present inventionfcon templates the selectivereception of the modulated high frequency oscillations, therectification of ,the selected oscillationstoseparate out the modulatingcomponent, the raising of the separated component by modulation with alocally generated wavef-to a an intermediate frequencyfhaving 'a valuethat permits ready ampli ficationi the amplifyingzoffthemodulatedintermediate frequencywave to such a degreeas may 1 beides'ired, and theseparation of the modulating component from the amplifiedintermediateQfrequency waye'by rectification 'drdetection. Furthermore,"the present invention relates to the provision of an improved"organization whereby the various steps in the abovje recited process ofreception and amplificationmay be effectively carried out, and whereincertainfof the parts-or l units of the organization are employed toefiect tWo or inoreof the steps in the sequence of opera- The inventionwill be-e'xplained in connection with the accompanying drawings, whichil1us-' trate certain preferred" and typical organizations wherebythedesired mode of operation may be realized. In'the 'representatiyecircuit organizations illustrated in the accompanying drawings,

Fig; 1 shows diagrammatically;radio receiving system whereinthe receivedhigh frequency imod ulated wave is intercepted 'b'y'a loop antenna,demodulated, the modulating component coma .binedwitha locally generatedintermediatejfre quency wave,-amplified.at the intermediate fre quency,and detected to produce the signal indie cation; Fig. 2 shows amodification in which an open or ordinary antenna is employed instead ofi r a loopfandin which the demodulation of the received high frequencyoscillations and'the subsequent combining of the modulating componentsand the locally generated intermediate frequency oscillations areeffected in a single modulating device; Fig. 3 shows'a furthermodification in which an ordinary antenna is employed [for intercepting.the received high frequency waves, and the first detection of themodulating components and their recombination with the localfromthedistant station are received .upon the loopantenna 10, which includesinits circuit the antenna winding ll of the-coupler-or radio frequencytransformer 12, and also the variable antennatuning condenser 15. Theradio .f'requency transformer 12 also includes'the secondary winding 13and the; feed back winding or tickler coil 14, andthe coupling relationbetween the three coils, of the radio frequency trans- I former; 12 ispreferably, made. variable as indi cated. Preferably the antenna coil 11consists .of only-,a few turns and islooselycoupled with the secondarycoil or winding 13. The termie nals of thesecondary coil 13 areconnected with theterminals of the variable tuning condenser 16, and oneof the terminals of this resonant tuning circuit is connected with thegrid of the thermionic detector tube 17 by way of theusual grid leak "76and condenser 77, while the otherterminal is connected with thepositive'terminal of the filamentof the detector tube 17; v:

.The plate of detector tube 17 is connected with the intermediatepositive pole of the B battery byway of the tickler coil 14, and theprimary winding of audio-frequencytransformer18'shunt ed by a highfrequency'by-pa-ss condenser 19'.

The secondary winding of the audio frequency.

transformer 18 is shunted ,by an intermediate frequency by passcondenser: 20, and one terminal is connected with the grid of themodulator tube 21 while the other terminal is connected through the pickup coil 23 of intermediate frequency oscillator 22 to the negative ;poleof the A battery. The grid ofxthe intermediate frequency oscillator tube2' l:is connected through winding 25 with the negative pole of the Abattery while the plate" of the j oscillatortubeis connected throughwinding 24 with the high potential posi-.-

tivepole of the B :battery. Thezosciliator condenser 26 is connectedbetween the terminals;

of the windings 24 and 25 that extend to the plateand grid respectivelyof oscillator tube Z'Z,

and the oscillatory circuit thus constituted is in ductively coupledwith-the pick up coil .23, the coupling being made variable so thattheamount of, energy communicated to its associated circuit by the pick-up-coil23 may be regulated andcon- V trolled;

The plate; modulator tube -2111s connected with the high potentialpositive pole of the B battery by way of the primary winding ofintermediate frequency transformer 28, andthe. secondaryv winding oftransformer 28 has shunted across its terminals a filter condenser 29which operates to make the intermediate frequency transformer selectiveof the intermediate frequency and its modulating side bands. Oneterminal of this'selective" circuit is connected with the grid ofintermediate frequency amplifier tube 30 while the other terminal isconnected with the series filament circuitof the tubes at such a pointas to give'the grid of intermediate frequency amplifier tube 30 theproper potential with respect to the associated filament.

The plate of intermediate frequency amplifier tube 30is connected withthe high potential positive pole of the B battery by way of the primarywinding .of intermediate frequency transformer 31, and the secondarywindingis included-in a circuit which, extends from the grid ofinterme-.

diate frequency amplifier tube'32' tov a point on the series filamentcircuit which gives the grid of tube22 its proper operating potential,The plate of tube 32 is connected with the high potential positive poleof the B battery through the primary winding of intermediate frequencytransformer 83, and the secondary winding of this transformer has oneterminal connected withthe grid of de- 'tector tube 34 through the usualgridileak 78 and condenser 79, while the other terminal of the secondarywinding of the transformer 33 isconnected to the positive terminal ofthe filament- 0f the associated detector tube34. The plate of detectortube 34' is connected with the intermediate positivepole of the Bbatterythrough; the head tele- 1 phones 35 or other receiving device,while the condenser 36 serves to'by-pass around the telethe platecircuit of detector tube 34,

In-the particular embodiment of the invention 7 it illustrated in Fig.1- the filamentsof thetubes are connected in series across the terminalsofftheA battery, with a rheostat 3'7 includedfor control ling thecurrent flow in thfeseries filament circuit. This series arrangement ofI the tube filaments',

,which is one that is known in the. art,;aifords .a

convenient means for securingthe-proper potential relation between eachfilamentand the grid of. the :cor responding tube. The condensers 38, 39and 40 are condensers of relatively large capacity for reducing theimpedance to the flow of alternating or. oscillatory currents in thepaths phone receiver thehigh frequencies appearing in thatare common tovarious parts of the circuit.

organization.

in Fig.1 is-as follows: 5 The received modulated high frequency wavescausetheflow of corresponding oscillatory currents in the circuit of theloop anteniia l lrthe .loop circuit being tuned to the frequency of theparticular station'desired by the variable tuning condenser 15, and theenergy of the selected high frequency wave being transferred to-the gridcircuit of the detector tube llaby the inductive coupling existingbetween the primary winding 11 and ofthe variable condenser 16 of theresonant grid circuit. The detector 17 operates in the usual '1 Theoperation of the organization illustrated .seconda'ryavinding 13 of thecoupling coil 12. Additional selectivity ;with respect-Ito the frequencythat iSutQ be received is obtained by means w'ay' to detect and separateout the modulating component of thereceived-high frequency wave, 1. 1

this low frequency-modulating component flowing ,through the primarywinding of audiofrequency transformer 18 while theamplified modulatedhigh frequencyoscillations flow in the circuit that includestheticklercoil 14 andthehigh frequency by-pass 19. Byproperly adjusting thecouplingof the tickler coil 14' with the grid coil 13', the action isadjusted to secure maximum regenerative effect with a correspondingamplifica tion .of the audio frequency modulating components thatfiow inthe primary .winding'of audio" frequency transformer 18. l

. The audio frequency components stepped up in potential appear in thesecondary winding of the audiofrequency transformer 18 and are appliedto the gridofmodulator tube 21 in combination with the intermediatefrequency oscillations .generated by, the oscillator'22. The constantsof the oscillatorp22 may be so adjusted as to produce a frequency. thatis above. audibility' and is low enough to avoid the difficultiesincident to the amplification of such frequencies. as: lie in theordinary radio frequency range. vA frequencyof,

say, 50,000 cycles per second is a convenient-frequency toemploy,.although other frequencies ly-. ing within the range of thesuperaudible and subradio frequencies maybeused.

i 'As a result of the modulating action of tube 21, there appears in theoutput circuit of the tube the intermediate frequency -'of theoscillator with its upper and lower side bands resulting from theintermodulation with the audio frequencies, and also a componentconsisting of amplified and unmodulated intermediate frequency. The

proportion of the modulated and unmodulated intermediate frequencycomponents may be reg- .ulatedto give the best results by an adjustjment of the oscillator pick up coil 23. r

. The intermediate frequency oscillation and its accompanying modulatedwave are communi mission of a frequency band based upon the 2intermediate frequency which the oscillator 22 has been adjusted togenerate. In the detector tube 34 the intermediate frequency with itsaccompanying modulating side bands aredemodulated to produce in theoutput circuit of the detector tube the audioor modulating frequencies,the high frequency products of demodulation being by-passed by way ofthe condenser 36.

The intermediate frequency oscillator and also the devices included inthe stages of intermediate frequency amplification are adjusted fortheproduction and transmission of the same intermediate frequency, andwhen the. rate of 0scillation of the intermediate frequency has beenchosen the setting of the oscillator for the production of thisfrequency is maintained, and is not varied for. each particular highfrequency modulated wave that is being received; The adjustment ofthereceiving system is thussim- .pler than in the case of asuperheterodynere ceiver.

Referring now to the'modification illustrated in Fig. 2, the antenna istuned to the desired frequency: by the variable. condenser 41, and thehigh frequency oscillatory current flowing in the antenna circuit setsup a corresponding flow in the grid circuit of tube 42 through themedium of theooupling existing between the. antenna coil and thegridcoil 8l of transformer 43. This coupling is made variable, as indicated,and the grid coil is shunted by variable condenser 44 in I nant to thesame frequency to which the r In consequence of order that thegridcircuit maybe-made resoantenna circuit has been "made selective."

The tube 42 acts as a regenerative amplifying anddetecting tube, andalsooperates to mod ulate together the detected low or audio frequencycomponents of the "received radio frequency wave and an intermediatefrequencygen erated by the intermediatefrequency; oscillatorThe'regenerative action of the tube '42 with" 45. respect to themodulatedradio frequency wave I is byvirtue oif the feed back connectionfrom the plate circuit of thetube by way of the tickler coil 82 oftransformer 43 and condenser 46ffiOith8 filament of the tube. 1 Thecondenser 46 isofs'uch capacity that the path in which it. is includedorfers'low impedance to the ,passage of, radio"fre quency currents andhigh impedance totheip'assage of intcr nediatefrequency andaudioffrequency currents. The radio frequency currents are preventedfrom being diverted into'gother branchesof the plate circuit bytheinterposition oftheradio frequency choke coil 4'7; The coupling of thetickler coil with the gridcircuit'winding of transformer 43 ismadevariable, asindicated.

42, the audio frequency componentsof the modulated high frequency Waveappear intheplate circuit of the tube. These audiov frequency cur-.rents pass freely through the? radio frequency the detecting action oftube choke coil 47, are .divertedfrom the branchin-I,

frequency transformer 48 and condenser 49, on account of the constantsof this path being such cluding the primary a winding .of intermediateasto make the path of high impedance to audio frequency currents and of'low impedance .to intermediate frequency currents, and pass. throughthe primary winding of .audio frequencytransformer 50. i The.corresponding audio, frequency currents which appear in the secondarywinding of transformer 50 are communicatedto a circuit including apotentiometer 51 and a pick upjcoil 83-of ,theintermediatefrequencyoscillator 15, i

this circuit also including the secondarywind .ing' 81. of transformer43 andturiing condenser. e

44, and terminating at the grid oftube 42; Cone sequently the detectedaudio frequency current and the intermediate frequency carrier are-applied to theinput circuit of tube 42, aremodulated together andv theproducts of 'modulation appear in the output circuit ofthe'tube. Byadjusting the potentiometer--51 and 'thevariable pick up coil 83of'oscillator 45 the amounts-of audio frequency and intermediatefrequency currentapplied to xthe gridxcircuit may be correctlyproportioned. The-condenser 52 acts as a bypass for the intermediatefrequencies around the impedance of the secondary winding, of audiofrequencytransformer' 50 and its 'po tentiometer i5l,jand the'condenser53jserves as a by-pass for the radio frequencyicur rent'around theimpedanceof that partcf the grid circuit 'includingthe pick upcoil83,0fjo'scillato1' 45 and the secondary winding f and potentiometer ofaudio frequency transformer 50. I

The intermediate frequency oscillations with their audio frequency" sidebands that now appear in the'output circuit of tube pass through theradio frequency choke coil 47 and the intermediate frequency lowimpedance path including the primary winding of intermediate frequencytransformer 43.and condenser; 49, being divertedfrom the path includingthe primary winding .of audio frequencyftransformer 50 on account of itshigh impedance to intermediate frequency oscillations. There is alsopresent in the output circuit of tube 42' reamplified audio frequencycurrents; but

these currents are prevented from singing 1 aroundthecircuit by theproper adjustment of potentiometer 51 and the oscillator pick up coil.

desired to transmit. Thencethe modulated intermediate frequencyoscillations pass through the intermediate frequency amplifying stagesincluding'amplifying tubes and 5'7 and intermediate frequencytransformers 56 and 58to the circuits 1 of. detector tube 59 where'theaudio frequency components of'the. modulated intermediate frequencyoscillations are detected andcornmunicated to the telephone or receivingdevice 62 after;

passing through the audiofrequency transformer 60. and audio frequencyamplifying tube 61. In.

other respects the circuit of'Fig; 2 corresponds withthat of Fig. 1 andneednot be'described in detail.

In the modification illustrated inFig. 3 use is made'of the principlesof the balanced modulator or detector, the type employed being generallythat disclosed in United States patent to Hartley No. 1,419,552 issuedJune s, 1922.. The reflex connections of this balanced modulator arealso generally. of the nature of those disclosed in the application ofFarrington and Smythe, Serial No. 654,104 filed July 27, 1923,alteredin'such a way as to provide forthecomplete demodulation of the receivedmodulated radio frequency .wave' and the'remodulation of the audiofrequency compoments into an intermediatefrequency carrier in thesame=modulatin'g device. In the ,modified' form of the inventionillustrated-in Fig. 3 the par-' ticular modulated high frequencyoscillations that it is desired 'to receive are selected and applied tothe common branch'of the input circuitsof modulatorv tubes 63 and'64through the medium of the input transformer 65, the secondary circuit ofwhich is tuned Iby'the variable condenser 66. The

modulated high frequency oscillations are applied in thesame phase tothe gridsof the modulator tubes '63 and or by way of the two inputcircuits each of which includes one of the two secondary windings of thetransformer G'Zshunted by their respective balancing and lay-passcondensers 68, and'leach of which includes the customary grid leakandcondenser; or, if desired, the modulating I action of the balanced tubesmay be secured by maintainingthe grids of the tubes at the propernegative potential with respect to their filaments by means of a 0battery or otherwise. I .As both the tubes 63 and 64 are operating inthe same phase, the detected audio frequency components of the modulatedwave are additive in the commonoutput circuit of the tubes. These audiofrequency components flow through the primary winding of audio frequencytransformer 69,

being diverted from the parallel branch includ ing condenser .70 andprimary winding of'intermediate frequency transformer 71 on account ofthe high impedanceof this branch to audio frequency currents, and arereproduced in the secondary winding of the ,audio frequency transformer69. From the secondary winding the audio frequency currents flow totheprimary winding oftransforme'r 6'7, being controlled in their magnitude by the potentiometer. 72; ,The secondary winding of transformer67 is so'connectedinthe input circuit of the balancedmodulatortube .63.

and 64 that the repeated audiofrequency'currents I are applied inopposite phase to the gridsof the two'tubes. At the sametimeintermediatefrequency oscillations generated by the intermediatefrequency oscillator Oand controlledin magnitude by the potentiometer'73 are applied to the common branch of the divided input circuit by.'way'of the transformer 74. As a result the products of intermodulationbetween the audiov frequency currents applied through transformer 67 andthe intermediate frequencycurrent" appear 'additively in the commonoutput circuit of-the two tubes, while the amplified. audio frequenciesapplied throughtransformer 6'7, appearing in opposite phase in theoutput circuit of the two tubes; are completely neutralized andsuppressed. The

two tubes operating in the same phase with respect to the intermediatecarrierfrequency, this frequency also appearsin the common outputcircuit of the tubes and accompanies the audio frequency side bands ofthe intermediate fre quency wave through the intermediate frequencyamplifiers that are representedby, the squares marked IFA. Theintermediate frequency and its side bands are demodulated in thedetector D,

and after amplification of the audio frequencies in the audio frequencyamplifier AFA, these'frequencies are passed to the receiving apparatus.

invention herein disclosed may be practiced in a variety of forms, andother of these forms are indicated skeleton in l, 5 and 1 6. In the formillustrated in Fig.4, the received frequencyniodulated wave is appliedto the input circuit of ajself-heterodynei or autodyne receiver, which,however, is adjusted to continuously generate oscillations of arelatively low or intermediate frequency. Consequently there are presentin the output circuit of the autofrom the demodulation, ofthereceived-high irequeney wave in the modulating oscillator; Thesefrequencies are selected and passed to the modu- 'dyne these continuousintermediatefrequencies" together with the audio frequencies resultinglater, which is shown next in the seriesof desighated squares, and inthis modulator thea'udio frequencies and the intermediate frequencyaremodulated together. After this the intermediate frequency with'its audiofrequency" side bands are passed through the two intermediate frequencyamplifiers that are indicated, to the detector, where final demodulationtakes place.

In the formillustrated in Fig. 5 the autodyne is reflexed' to act alsoas'a modulator to recombine the intermediatefrequencies which itgencrates with the audio frequencies which are set I free from themodulated high frequency wave by virtue of the detecting properties ofthe autodyne, the recombined and intermodulated intermediate and audiofrequencies appearing in the- .cutput circuit and being passedthIOllg'hjtWO stages 01 intermediate frequencyamplification-to thedetector.

In the modification illustrated in Fig. 6, one

stage of radio frequency amplification "precedes the detection of theaudio frequencycomponents of the received high frequency oscillations.From the detector the audio frequencies, either'iwith or withoutfurtheramplification into theinput circuit of a modulator of'thewell-known Heising type where they are modulated with a carrier wave ofintermediate frequency within the readily ampliiiable range. Aftermodulation,

the modulated intermediate frequencies passj through one or morestagesof intermediate fre' quency amplification tothe detector.

TheLpresent invention, as described abovaf makes it possible totranslate received modulated radio frequency waves in a radio'frequencychannel into readily amplifiable intermediate frequeficy waves inanintermediate frequency channel and to prevent undesired reactionsbetween waves in the radio frequency and intermediate frequency channelsby interposing a low frequency channel therebetween. Difficultiesexperienced in superheterodyne systems from reactions between the highfrequency and intermediate frequency circuits are thus avoided, Furtheradvantages of the present invention are that the frequency of the localoscfllations may be easily adjusted without critical operations and theinitial adjustment of the oscillator frequency serves for all receivedwave frequencies. The invention also provides a method different fromthat of the superheterodyne system for attaining advantageous resultsheretofore obtainable only with the superheterodyne system.

It will be understood that in the various modi fications of theinvention illustrated and described, theamount cf amplification at thehigh frequency, intermediate frequency and low or ,audio frequencylevelsmay be provided as defied energy.

lated wave. I a a 4. The method of amplifying received high frequencyelectrical wave energy and of minimiz sired to produce the bestoperation of the sys-' tem under varying conditions with respect to thenature and amount of the received energy and the nature and amount ofenergy required to be.

made avai able in the audio frequency responsive device; Y

The invention claimed is: 1. The methodof amplifying high frequencyelectrical wave energy which comprises translating said high frequencywave energy into low frequency waves, supplying intermediate frequencywaves having materially less tendency to radiate than said highfrequency waves, modulating said intermediate frequency waves with saidlow frequency waves, amplifying the resulting modulated intermediatefrequency waves,

and translating said amplified intermediate 'fre-' quency waves into lowfrequency waves of ampli- 2. The method of amplifying high frequencyelectrical wave energy modulated in accordance with low frequencymodulating waves, which comprises reproducing said low frequencymodulating waves by rectification of said high frequency wave energy,supplying readily amplifiable intermediate frequency waves, modulatingsaid intermediate frequency waves with said low frequency waves,amplifying said modulated intermediate frequency waves, and reproducingsaid modulating waves with amplified energy by rectification of saidamplified intermediatev frequency waves. 7 I

3. The method of indirectly amplifying the modulating wave with whichanincoming modulated high frequency electric wave has been modulated,which comprises reproducing said modulating wave by demodulating saidhigh frequency wave, supplying a readily amplifiable wave of frequencyabove the audible range, but too low to permit of substantial radiation,modulating 'said intermediate frequency wave with saidre produced wave,and amplifying said last modu} ing the introduction of disturbances,-which method comprises producing' lowfrequency waves of amplified"energy under the control of; said high frequency wave'fenergy forobtaininga part of the desired; amplification, supplying inter: mediatefrequency, waves, modulating said inter mediate frequency Waves withsaid low frequency- 1, waves of amplifiedenergy to produce'modulated5.-The method of translating-signal waveen ergy of. high frequency intosignal waves of intermediate frequency and of'preventing undesirablereactions between said signal waveenergy of high, frequency and saidcorresponding sigintermediate frequency waves "of amplified em ergy,and: amplifying said modulated intermedi ate'frequency waves forobtaining the remain- J ing'part of the desired amplification,{- i

nal waves of intermediate frequency, said meth- I od consisting intranslating said signal wave en:

ergy of highfrequency into signal waves of 10w frequency beforetranslation into saidintermediate frequency waves, and then producingsaid intermediate frequency waves by translatio frequency waves intoamplified low frequency J waves.

7, In a system for receivinghigh frequency T Waves, a modulator, means,whereby high frequency waves modulated in accordance with low frequencywaves are selectively transmitted to saidmodulator, a' local source ofsuper-audible,

non-radiating intermediate frequency waves, said modulator being adaptedto demodulate said high frequency waves to reproduce said lowfreducedlow frequency waves, means for amplifying the" resulting modulatedintermediate frequency waves, and means for utilizing-the resultingamplified intermediate frequency waves.

,8. In a radio receiving system, meansfor selectively receiving audiofrequency modulated radio frequency waves, a source of intermediatefrequency waves, the frequency of said intermedi- [quency waves and tomodulate intermediate frequency wavesfrom said source with said reproatefrequency waves being so low and'said system being so designed thatsubstantially no in;

termediate frequency waves are radiated, a mod- .fulator whereby theselected radio frequency waves are demodulated to reproduce the audio.frequency modulating waves and whereby said intermediate frequencywaves are modulated with said reproduced audio frequency waves, anamplifier for said modulated intermediate frequency waves, and ademodulator for said amplified intermediate .frequencywaves forreproducing said audio frequency waves with amplified is energy.

' 9. In a wavereceiving system, a thermionic modulating device havinginput andoutput 'circuits, means for impressing a received signalmodulated high'frequency wave upon said input. circuit, a localintermediate frequency wave source, means for impressing upon saidinputv circuit,-a,t-hermionic intermediate frequehcy-am-x circuit thewavegfrom said-local--source together V 'tenna, meanscoupled to saidantenna for de-x with the detected :signals, present-in said outputplifier coupled with said modulatingidevice, and

55a detector'coupled with'saidintermediate frefquency amplifier 7whereby the amplified intermediate frequency waves aredemodulated tore-v V produce amplifiedsignals;

intermediate frequency :below the eflective 'fre'-.

quency receivingor radiating range of said an-:'-

modulating the received highfrequency wavesto roduce lowirequency "wavesand for modulatg,

ing waves from said source with said low fre quency waves, means, forselecting the resulting EDWIN H. SMYTHEQV with amplified energy. 85

